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// Package stack implements a simple LIFO Stack for generic values
package stack

// Value is a generic value
type Value interface{}

// Stack contains generic values
type Stack []Value

// NewStack returns a new Stack
func NewStack() Stack {
	return Stack{}
}

// Push adds value at tail
func (s *Stack) Push(v Value) {
	*s = append(*s, v)
}

// Insert inserts value at head
func (s *Stack) Insert(v Value) {
	*s = append(Stack{v}, *s...)
}

// Pop retrieves value from tail
func (s *Stack) Pop() (v Value) {
	if size := len(*s); size > 0 {
		v, *s = (*s)[size-1], (*s)[:size-1]
	}
	return v
}

// Peek returns top value from Stack
func (s Stack) Peek() Value {
	return s[len(s)-1]
}

// Swap swapes two top values
func (s Stack) Swap() {
	if size := len(s); size >= 2 {
		s[size-1], s[size-2] = s[size-2], s[size-1]
	}
}

// Depth returns actual size of Stack
func (s Stack) Depth() int {
	return len(s)
}